King was born on 15 July 1809 at Stonehouse, Devon, the second son of Vice-Admiral Sir Richard King and Sarah Anne née Duckworth.[2] He was educated at Royal Naval College, Portsmouth.[2]
King married Lady Caroline Mary Dawson Damer in 1847.[2] He assumed the arms and prefix surname of the Duckworth family from Admiral Sir John Duckworth, his grandfather, in 1888.[4] King died at his home Wear House in Exeter, Devon, on 18 August 1891 aged 82.[2] He was buried in a new vault at Topsham Cemetery, Exeter on 25 August 1891.[5]